How to show Linux version

[root@akwal ~]#  cat /etc/*-release

                    CentOS release 6.3 (Final)

OR


[root@akwal ~]# cat /etc/issue

                   CentOS release 5.5 (Final)
                   Kernel \r on an \m

[root@akwal ~]# lsb_release -a


     LSB Version: :core-3.1-ia32:core-3.1-noarch:graphics-3.1-ia32:graphics-3.1-noarch
     Distributor ID: CentOS
     Description: CentOS release 5.5 (Final)
     Release: 5.5
     Codename: Final